Advantages and disadvantages of using key shapes to correct pose of a scene
A shape key is a difference effect on a mesh.
So for better controlling faces, or elbows  or shoulders etc.
You can add shape keys, their effect is visible based upon their weight setting. So setting their weight value back to zero will return your original mesh again.

If you worked with linked blend files, sure then you would need to reload(update) if you do this a lot in post production. However one can also create several situations first (angry face/happy etc).
Alternatively if its only a few characters you dont link it, but import it.   

BTW its an interesting video that you found!